I'm getting ready to pull the lg4 and manual transmission from a 82 z28 and swap it Into a 89 firebird. The z28 has discs on the rear though the firebird has drums. How common were the rear discs? Would it be worth the trouble of swapping rears?

 

As far as I know, disc brakes was NOT an option for the 82 at all. 1987 was the 1st year for rear disc brakes for the camaro.

It was a performance option where you had to get the G92 option. A lot of the TPI engine cars got the rear disc but thats still pretty limited.

Yes it is worth swapping the rear end for a few reasons.
If it has disc brakes then it's probably safe to say it's an '87 or later rear end which means the ring gear is larger at 7-5/8" vs the 7-1/2" so a little stronger.
The disc brakes are better than drums.

It could also be a 9 bolt borg warner rear end which is stronger than the GM 10 bolts.

If you swap the rear over you will need to swap the prop valve (under master cyl) off the disc brake car as well

 

Four-Wheel Power Disc Brakes Were Available From 1982-1992 Either As An Individual Option Or In A Performance Axle Package.

 

Hmmm cool. Thanks for that info. I did not know that. I though it was just an option for the 87 and up or so as that's the only ones I have ever seen with factory 4 wheel disc

 

The 70 through 88 rear disc are really not worth the swap in my opinion...

 

Not sure of the '82-'88 rear discs, but in the early 80's I put a '79 TA rear disc under my ''78 Camaro...excellent and even stopping power, no more rear wheel lock ups, etc...was quite an improvement.

 

Right, they'll "work" for awhile. But the calipers are just a terrible design with their screw in piston that's failure prone.